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arXiv 1909.08550astro-ph.GA
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$z<1$被动演化星系和恒星形成星系的三维形状演化

Evolution of 3-dimensional Shape of Passively Evolving and Star-forming Galaxies at $z<1$

Yuki K. Satoh, Masaru Kajisawa, Kazuharu G. Himoto

备注：
43 pages, 41 figures, accepted for publication in ApJ
发表信息：
The Astrophysical Journal, Volume 885, Issue 1, article id. 81, 35 pp. (2019)
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摘要：

利用HST/ACS $I_{\rm F814W}$波段数据，研究了宇宙场中$M_{V}<-20$在$0.2<z<1.0$的$\sim21000$星系视轴比随恒星质量、比恒星形成率（sSFR）和红移的变化。我们统计估计这些星系的内在三维形状拟合的轴比分布与三轴椭球模型，其特征在于面对（中长）和边缘（短到长）的轴比$B/A$和$C/A$。我们发现，从薄盘到厚球体的转变发生在$Δ$ MS $\sim-1$ dex处，即，对于在$0.2<z<1.0$具有$M_{\rm star} = 10^{10}$ -- $10^{11} M_{\odot}$的星系，sSFR比主序星低10倍。此外，与$M_{\rm star}=10^{10}$ -$10^{11}M_{\odot}$的被动演化星系的固有厚度（$C/A$）显着减少随着时间的推移，从$C/A \sim 0.40$ - $0.50$在$z\sim 0.8$ $C/A\sim0.33$- $0.37$在$z\sim0.4$，而那些星系与$M_{\rm star}>10^{11}M_{\odot}$有$C/A\sim0.5$的红移无关。另一方面，在主序列上的恒星形成星系与$10^{9.5}$- $10^{11}M_{\odot}$在$0.2<z<1.0$的形状没有显着的演变，但它们的厚度取决于恒星质量;更大质量的恒星形成星系往往有较低的$C/A$（更薄的形状）比低质量的。这些结果表明，$z\sim1$周围开始出现的一部分薄盘状恒星形成星系在没有剧烈形态变化的情况下淬灭了它们的恒星形成，而这些新增加的相对薄盘状静止星系导致了$z<1$附近具有$M_{\rm star}<10^{11}M_{\odot}$的被动演化星系轴比分布的显著演化。

英文摘要：

Using the HST/ACS $I_{\rm F814W}$-band data, we investigated distribution of apparent axial ratios of $\sim21000$ galaxies with $M_{V}<-20$ at $0.2<z<1.0$ in the COSMOS field as a function of stellar mass, specific star formation rate (sSFR), and redshift. We statistically estimated intrinsic 3-dimensional shapes of these galaxies by fitting the axial-ratio distribution with triaxial ellipsoid models characterized by face-on (middle-to-long) and edge-on (short-to-long) axial ratios $B/A$ and $C/A$. We found that the transition from thin disk to thick spheroid occurs at $Δ$MS $\sim-1$ dex, i.e., 10 times lower sSFR than that of the main sequence for galaxies with $M_{\rm star} = 10^{10}$--$10^{11} M_{\odot}$ at $0.2<z<1.0$. Furthermore, the intrinsic thickness ($C/A$) of passively evolving galaxies with $M_{\rm star}=10^{10}$--$10^{11}M_{\odot}$ significantly decreases with time from $C/A \sim 0.40$ -- $0.50$ at $z\sim 0.8$ to $C/A\sim0.33$ -- $0.37$ at $z\sim0.4$, while those galaxies with $M_{\rm star}>10^{11}M_{\odot}$ have $C/A\sim0.5$ irrespective of redshift. On the other hand, star-forming galaxies on the main sequence with $10^{9.5}$--$10^{11}M_{\odot}$ show no significant evolution in their shape at $0.2<z<1.0$, but their thickness depends on stellar mass;more massive star-forming galaxies tend to have lower $C/A$ (thinner shape) than low-mass ones. These results suggest that some fraction of star-forming galaxies with a thin disk, which started to appear around $z\sim1$, quench their star formation without violent morphological change, and these newly added quiescent galaxies with a relatively thin shape cause the significant evolution in the axial-ratio distribution of passively evolving galaxies with $M_{\rm star}<10^{11}M_{\odot}$ at $z<1$.

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